It was the second such attack on an office of the Islamist group on Friday. The first was in the Cairo neighborhood of Manial.

Both attacks happened as opponents and supporters of the Brotherhood clashed near the group's headquarters in Cairo.

An Associated Press cameraman saw protesters attack the office in Alexandria, leaving with computers, files and other objects. The attack took place near the site where unknown assailants fought protesters demanding the resignation of President Mohammed Morsi, who is a member of the party.

Brotherhood offices came under attack across Egypt last December.

The group has characterized the assailants as "thugs" and "counter-revolutionaries" seeking to oust the democratically elected leader.